As the popularity of plastic, as opposed to glass, spectacle lenses has grown, ways have been sought to form these products in more efficient ways. For example, lenses are known to be formed by casting a layer onto a preform, or wafer, so that subsequent machining and processing can be significantly reduced, if not totally avoided.
However, as is obvious, a spectacle lens that has been carefully prescribed must be equally carefully manufactured. If the various angles in the lens are not as prescribed by the attending ophthalmologist or optometrist, the lens will not provide the benefits sought for the user and, in fact, could actually prove detrimental. Therefore, while more efficient methods of formation have been sought, this efficiency must not be obtained at the cost of accuracy.
In one manufacturing method, production of a spectacle lens requires one or more mold halves, a resin material employed to form one or more layers of the lens, and a preform. In the prior art, no mechanical fixture, or comparable device, had been developed to hold the mold and the preform in an exact set position to assure both accuracy and reproducibility of the cast layer. While a tolerance of xc2x11/2xc2x0 is the acceptable deviation for products of this type, the practically unregulated equipment of the prior art provided deviations of xc2x12xc2x0.
In accordance with the present invention, a device has been developed that allows fine control of the height (thickness) of a lens and the accurate control of the various angles specified for the spectacle lenses. Careful, and reproducible, control of each of these parameters is provided for in the fixture made in accordance with the present invention.
In general, the fixture of the present invention involves a bottom portion into which a mold half, preferably a female mold half, is placed. The bottom portion provides support so that the mold half will remain level and allow for the mold angles to be accurately controlled and reproduced. Movably mounted above the bottom portion that holds the mold half is a top portion, having two horizontal, plates adapted to slide relative to each other to control the X direction and Y direction. It also holds the preform or wafer and means are provided on this top portion to control the angular relationship of the mold half to the preform. For purposes of the invention, by xe2x80x9coptical preformxe2x80x9d or xe2x80x9cpreformxe2x80x9d means a shaped, optically transparent article capable of refracting light and suitable for use in producing a spectacle lens.
Means are provided on the fixture, not only for the accurate setting and indication of each of the relationships, but also for holding the dimensions and relationships constant in order to produce a series of lenses with the same angles and dimensions and without readjusting the equipment.